How to identify Faceted Gemstone

To correctly identify Faceted Gemstone (Unknown Gemstone (possibly Sapphire or Spinel based on color and cut)), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Typically blue, ranging from light sky blue to deep royal blue. Other colors are possible for both sapphire and spinel, but the context suggests blue.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to adamantine.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, polished surface due to faceting.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Faceted, meaning it has been cut and polished into a specific geometric shape to enhance its brilliance and color. Natural crystal forms for sapphire are typically hexagonal prisms or bipyramids; for spinel, they are commonly octahedra or dodecahedra.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Sapphire has no true cleavage but exhibits parting along basal planes or rhombohedral planes. Spinel has imperfect octahedral cleavage, but it is rarely observed in faceted stones.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Primary deposits in metamorphic rocks (marbles, gneisses, schists) and igneous rocks (basalts, syenites, peridotites). Secondary alluvial deposits are common for both due to their durability.

Key Facts

Hardness

Sapphire: 9 (Mohs); Spinel: 8 (Mohs)

Specific Gravity

Sapphire: 3.95-4.03; Spinel: 3.58-3.61

Crystal System

Sapphire: Trigonal; Spinel: Isometric (Cubic)

Color

Blue (most common for this description), but can be various colors for both minerals.

Luster

Vitreous to adamantine

Transparency

Transparent to translucent

Fracture

Conchoidal to uneven

Cleavage

Sapphire: No true cleavage, but parting; Spinel: Imperfect octahedral cleavage

Composition

Sapphire: Aluminum Oxide (Al2O3); Spinel: Magnesium Aluminum Oxide (MgAl2O4)

Physical characteristics

• Crystal Habit: Faceted (cut from natural crystals which are typically hexagonal prisms/bipyramids for sapphire, and octahedra/dodecahedra for spinel)
• Cleavage Type: Sapphire: Parting on {0001} and {1011}; Spinel: Imperfect octahedral on {111}
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to adamantine

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